Separation of cyclic and acyclic hydrocarbons by extractive distillation



May 8, 1962 E. c.- MAKlN, JR 3,033,763

SEPARATION OF CYCLIC AND ACYCLIC HYDROCARBONS BY EXTRACTIVE DISTILLATIONFiled Oct. 31, 1958 EARLE'C- MAKIN JR.

INVENTOR.

BMW

ATTORNEY 3,033,753 Fatented May 8, 1962 This invention relates to theseparation of mixtures of hydrocarbons and more particularly to theseparation of mixtures of acyclic and cyclic hydrocarbons containing sixcarbon atoms.

Aromatic hydrocarbons can be prepared by the dehydrocyclization ofaliphatic hydrocarbons containing six carbon atoms. Petroleum refinerystreams can be treated or processed to produce a mixture of hydrocarbonscontaining six carbon atoms. Such a mixture, when obtained byconventional operations, contains acyclic, alicyclic and aromatichydrocarbons. In order to efiiciently dehydrocyclize the C acyclichydrocarbons to aromatics it is necessary that the alicyclicsubstituents of the hydrocarbon mixture be removed. Due to the closenessof the boiling points of the various isomeric C hydrocarbons present insuch mixtures obtained by the more conventional methods of operation,such a separation is most diflicult. 1

It is an object of this invention to provide an improved method for theseparation of cyclic hydrocarbons from a hydrocarbon mixture consistingessentially of acyclic and cyclic hydrocarbons each containing sixcarbon atoms. Additional objects will become apparent from thedescription of the invention.

It has now been discovered that cyclic hydrocarbons contained in a feedmixture consisting essentially of acyclic and cyclic hydrocarbons eachcontaining six carbon atoms can be effectively separated from said feedmixture by an extractive distillation process which comprisescontinuously introducing said feed mixture into an intermediate sectionof a fractionating column, continuously introducing a solvent into saidfractionating column at a point above the point of introduction of saidfeed mixture so that said solvent flows countercurrent to and intimatelycontacts the ascending vapors of said feed mixture, withdrawing overheada mixture of acyclic hydrocarbons substantially free of cyclichydrocarbons and removing from the bottom section of said column asolution of cyclic hydrocarbons contained in said solvent, said solventintroduced into said fractionating column being a mixture comprisingfrom about 90 to about 50 volume percent of phenol and from about 10 toabout 50 volume percent of a glycol having the formula HOROH wherein Rrepresents a radical selected from the group consisting of alkylene andoxa-alkylene radicals having a molecular weight from 28 to 116.

The invention may be illustrated by reference to the drawing in which anembodiment of the invention is schematically represented. A feed mixtureof hydrocarbons to be separated is introduced into fractionating column1 through line 2. The liquid in the lower part of the column isvaporized by heat supplied by reboiler 4. The solvent is introduced inthe liquid phase at the top of the column through line 3 and flows downthe column countercurrent to the rising vapors. The vapors passingupwardly through the descending solvent are withdrawn overhead throughline 5, passed through condenser 6 where they are liquified, a portionreturned to the column through line 8 as reflux and a portion recoveredthrough line 7 for further use and/or processing. The solvent havingdissolved therein cyclic hydrocarbons is removed from the column throughline 9 and the cyclic hydrocarbons recovered if desired.

The following examples are specific illustrations of the novel processof this invention:

Example I In order to effect the separation of hydrocarbons inaccordance with the processof this invention a fractionating columncontaining 60 perforated trays was employed. The hydrocarbon feedmixturehad the following composition:

Hydrocarbon: Volume percent Z-methylpentane 7.1 S-methylpentane 10.1n-Hexane 49.5

Methylcyclopentane 14.1 Cyclohexane 15.2 Benzene 3.5 2,4-dimethylpentane0.5

Hydrocarbon: Volume percent Z-methylpentane 11.4 3-methylpentane 18.4n-Hexane 69.3 Methylcyclopentane Trace Cyclohexane none Benzene None2,4-dimethylpentane 0.9

Example 11 The procedure set forth in Example I was repeated using thesame hydrocarbon mixture specified therein. The solvent comprised volumepercent of phenol and 15 volume percent ethylene glycol. The solventfeed temperature was 80.281.0 C. and the pot temperature was 124.7-125.5C. The volume ratio of solventzoil was 8.0210 The column was operated ona continuous basis at a reflux ratio of 5: 1. The distillate,representing 59 volume percent of the feed mixture, had the follow-Hydrocarbon: Volume percent Z-methylpentane 11.2 3-methylpentane 17.9n-Hexane 69.2 Methylcyclopentane Trace Cyclohexane None Benzene None2,4-dimethylpentane 1.7

Example III The procedure set forth in Example I was repeated using ahydrocarbon feed mixture having the following composition:

The solvent was a mixture comprising 80 volume percent phenol and 20volume percent ethylene glycol. The solvent feed temperature was77.2-79.5 C. and the pot temperature was l24.9l34.8 C. The volume ratioof solventzoilwas 8.:O:1.0. The column was operated on a continuousbasis and operated at a reflux ratio of l.'

The distillate, representing 45 volume percent of the feed, had thefollowing composition:

Hydrocarbon: Volume percent 2-methylpentane 16.4 3-methylpentane 17.3n-Hexane 62.2 Methylcyclopentane 0.9 Cyclohexane None Benzene None2,4-dimethylpentane Trace Example IV The procedure set forth in ExampleI is repeated using the hydrocarbon feed mixture specified therein and asolvent mixture comprising 85 volume percent phenol and volume percenttriethylene glycol. The distillate is substantially free of cyclichydrocarbons.

Example V The procedure set forth in Example I is repeated using thehydrocarbon feed mixture specified therein and a solvent mixturecomprising'75 .volume percent phenol and volume percent propyleneglycol. The distillate .is substantially free of cyclic hydrocarbons.

Example VI The procedure set forth in Example I is repeated using thehydrocarbon feed mixture specified therein and a solvent mixturecomprising 60 volume percent phenol and 40 volume percent diethyleneglycol. The distillate is substantially free of cyclic hydrocarbons.

Example VII The procedure set forth in Example I is repeated using thehydrocarbon feed mixture specified therein and a solvent mixturecomprising 90 volume percent and 10 volume percent dipropylene glycol.The distillate is substantially free'of hydrocarbons.

As a solvent for the novel process of this invention and glycol havingthe formula HOR--OH wherein R represents a radical selected from thegroup consisting of alkylene and oxa-alkylene radicals having amolecular Weight from 28 to 116 may be mixed with phenol in theheretofore set forth proportions. The glycols that'can be used in theprocess of this invention include ethylene glycol, propylene glycol,tetramethylene glycol, pentamethylene glycol, hexamethylenc glycol,diethylene glycol, triethylene glycol, dipropylene glycol and so forth.

a Any fractionating column of conventional design providing -forcountercurrent liquid-vapor contact under reboiling and refluxingconditions may be employed. The column can be a packed column or it canbe equipped with perforated plates or bubble cap trays. The number oftheoretical plates in the column depends on efiiciency'of separationdesired, the precise composition of the feed mixture, the quantity ofsolvent, the reflux ratio, and other related factors well known to thoseskilled in the art. Under certain conditions five theoretical plates areadequate while under more adverse conditions as high as a hundredtheoretical plates may be required.

The-hydrocarbon feed mixture separated in accordance with this inventionconsists essentially of acyclic and cyclic hydrocarbons all containingsix carbon atoms. Very small amounts of otherhydrocarbons can betolerated in the mixture but such hydrocarbons should be kept to aminimum as they can interfere With the efiiciency of this particularextractive distillation.

The hydrocarbon feed mixture is preferentially introduced into thefractionating column in an intermediate section. The solvent isintroduced at a point above the introduction of the hydrocarbon feedmixture and preferably near the top of the column. Both solvent andhydrocarbon feed mixture are introduced continuously. The solvent feedtemperature can vary substantially and is adjusted to maintain steadystate conditions in the column.

The quantity of solvent required to be introduced, continuously into thecolumn in order to accomplish the desired separation can vary overrather wide limits depending upon the efiiciency of separation desired.Generally, at least two parts by volume of solvent for each part byvolume of hydrocarbon mixture is necessary to effect any eflicientdegree of separation. The quantity of solvent used can be increased toas high as 10 and at times even as high as 20 volumes per volume ofhydrocarbon mixture. As dilution of the internal reflux becomesinfinite, separation becomes sharper but operating efficiency is loweredconsiderably because of the relatively small quantity of hydrocarbonfeed mixture being processed as in finite reflux is approached. Toolarge an excess of solvent is, therefore, to be avoided.

Although generally the extractive distillation of this invention is tobe carried out at about atmospheric pressure, as illustrated in theexamples, it may be conducted below, or above atmospheric pressure.

The reflux ratio can be varied considerably in the proper operation ofthis extractive distillation process and the exact ratio will bedependent upon the operating characteristics of the column, the quantityof solvent employed and the degree of separation desired.

The cyclic hydrocarbons contained in the solvent can be recovered by anytechnique well known to those skilled in the art. Generally, a simpledistillation is all that is required.

What is claimed is:

1. A continuous process for the separation of cyclic hydrocarbons from ahydrocarbon feed mixture consisting essentially of acyclic and cyclichydrocarbons all containing six carbon atoms which comprisescontinuously introducing said feed mixture into an intermediate sectionof a fractionating column, continuously introducing a solvent into saidfractionating column at a point above the point of introduction of saidfeed mixture so that said solvent flows countercurrent to and intimatelycontacts the ascending vapors of said feed mixture, withdrawing overheada mixture of acyclic hydrocarbons substantially free of cyclichydrocarbons and removing from the bottom section of said column asolution of cyclic hydrocarbons contained in said solvent, said solventintroduced into said fractionating column being a mixture comprisingfrom about to about 50 volume percent of phenol and from about 10 toabout 50 volume percent of a glycol having the formula HO--R-OH whereinR represents a radical selected from the group consisting of alkyleneand oxa-alkylene radicals having a molecular Weight from 28 to 116 andsaid solvent being introduced into the column at a solvent to feed ratioof about 2:1 to 20:1.

2. The process as described in claim 1 wherein the glycol is ethyleneglycol.

3. The process as described in claim 1 wherein the glycol is triethyleneglycol.

4. The process as described in claim 1 wherein the glycol is propyleneglycol.

References Cited in the file of this patent UNITED STATES PATENTSVoorhees Aug. 8, 1939 Deanesly July 21, 1942 Semon Jan. 2, 1945 10 6Gage Feb. 27, 1945 Lake Aug. 27, 1946 Rittenhouse Feb. 4, 1947 Shiras etal. Feb. 8, .1949 Boyd Sept. 2, 1952 Lavander Dec. 25, 1956 Cier et a1.June 23, 1959 OTHER REFERENCES Weissberger: Distillation, pages 325-340(1951).

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,033,763 May 8 1962 Earle C, Malkin J12,

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 2., line 541 after "fo11ow" insert ing composition: column 3 line53 after percent" insert phenol same column, line 57 for 'and read anySigned and sealed this 28th day of Augustv 19620 (SEAL) Attest:

ESTON Go JOHNSON DAVID L. LADD Attesting Officer Commissioner of Patents

1. A CONTINUOUS PROCESS FOR THE SEPARATION OF CYCLIC HYDROCARBONS FROM AHYDROCARBON FREED MIXTURE CONSISTING ESSENTIALLY OF ACYCLIC AND CYCLICHYDROCARBONS ALL CONTAINING SIX CARBON ATOMS WHICH COMPRISESCONTINUOUSLY INTRODUCING SAID FEED MIXTURE INTO AN INTERMEDIATE SECTIONOF A FRACTIONATING COLUMN, CONTINUOUSLY INTRODUCING A SOLVENT INTO SAIDFRAACTIONATING COLUMN AT A POINT ABOVE THE POINT OF INTROUDCTION OF SAIDFEED MIXTURE SO THAT SAID SOLVENT FLOWS COUNTERCURRENT TO AND INTIMATELYCONTACTS THE ASCENDING VAPORS OF SAID FEED MIXTURE, WITHDRAWING OVERHEADA MIXTURE OF ACYCLIC HYDROCARABONS SUBSTANIALLY FREE OF CYCLICHYDROCARBONS AND REMOVING FROM THE BOTTOM SECTION OF SAID COLUMN ASOLUTION OF CYCLIC HYDROCARBONS CONTAINED IN SAID SOLVENT, SAID SOLVENTINTRODUCED INTO SAID FRACTIONATING COLUMN BEING A MIXTURE COMPRISINGFROM ABOUT 90 TO ABOUT 50 VOLUME PERCENT OF PHENOL AND FROM ABOUT 10 TOABOUT 50 VOLUME PERCENT OF A GLYCOL HAVING THE FORMULA HO-R-OH WHEREIN RREPRESENTS A RADICAL SELECTEDFROM THE GROUP CONSISTING OF ALKYLENE ANDOXA-ALKYLENE RADICALS HAVING A MOLECULAR WEIGHT FROM 28 TO 116 AND SAIDSOLVENT BEING INTRODUCED INTO THE COLUMN AT A SOLVENT TO FEED RATIO OFABOUT 2:1 TO 20:1.